Nicotine dependence is highly prevalent among drug- and alcohol-dependent patients. A multisite clinical trial of smoking cessation (SC) treatment was performed at outpatient community-based substance abuse rehabilitation programs affiliated with the National Drug Abuse Treatment, Clinical Trials Network. Cigarette smokers (N=225) from five methadone maintenance programs and two drug and alcohol dependence treatment programs were randomly assigned in a 2:1 ratio to receive either (1) SC treatment as an adjunct to substance abuse treatment-as-usual (TAU) or (2) substance abuse TAU. Smoking cessation treatment consisted of 1 week of group counseling before the target quit date and 8 weeks of group counseling plus transdermal nicotine patch treatment (21 mg/day for Weeks 1-6 and 14 mg/day for Weeks 7 and 8) after the target quit date. Smoking abstinence rates in SC, 10%-11% during treatment and 5%-6% at the 13- and 26-week follow-up visits, were significantly better than those in TAU during treatment (p< .01). In addition, SC was associated with significantly greater reductions as compared with TAU in cigarettes smoked per day (75% reduction, p< .001), exhaled carbon monoxide levels (p< .001), cigarette craving (p< .05), and nicotine withdrawal (p< .05). Smoking cessation did not differ from TAU on rates of retention in substance abuse treatment, abstinence from primary substance of abuse, and craving for primary substance of abuse. Compliance with SC treatment, moderate at best, was positively associated with smoking abstinence rates. Smoking cessation treatment resulted in significant reductions in daily smoking and modest smoking abstinence rates without having an adverse impact on substance abuse rehabilitation when given concurrently with outpatient substance abuse treatment. Substance abuse treatment programs should not hesitate to implement SC for established patients.